1. Field of the Invention
The invention pertains to an inkjet printing apparatus having an array of inkjet print heads, wherein each print head has at least one ink port for receiving ink, at least one nozzle for directing ink onto a substrate to be printed, and at least one control terminal for receiving a supply voltage and/or control signals, and wherein a print head mounting element positions the print heads in a defined orientation relative to each other.
2. Description of the Related Art
In printing presses which operate according to the offset printing principle, especially web-fed rotary presses and sheet-fed presses, increasing use is being made of inkjet printing devices primarily for the purpose of individualizing the printed materials produced by offset printing by adding to them, for example, barcodes, numbering, or other types of labeling. These inkjet printing devices have at least one inkjet print head, which can be designed according to the so-called “continuous” inkjet principle, the drop-on-demand inkjet principle, the thermal inkjet principle, the bubble inkjet principle, or any of the other inkjet principles. The inkjet print heads usually have a row of nozzles consisting of several adjacent ink nozzles, through which the ink can be directed onto the substrate to be printed.
In many applications of inkjet printing devices, it is necessary to use a large number of inkjet print heads, some arranged transversely to the transport direction of the printing stock, i.e., transversely to the printing direction, and others arranged in the printing direction. The required number of inkjet print heads transverse to the printing direction is defined primarily by the desired print resolution in relation to the given print resolution of the selected inkjet print head and by the desired overall printing width relative to the printing width of an inkjet print head. The required number of inkjet print heads in the printing direction is determined primarily by two factors: first, the fact that the desired printing speed is greater than the given printing speed of an inkjet print head, and, second, the fact that several different printing inks are to be applied to the substrate by the inkjet printing device.
In this type of inkjet printing apparatus with a plurality of inkjet print heads, the inkjet print heads are arranged in an array-like or matrix-like manner, where, to increase the print resolution transversely to the printing direction, the inkjet print heads of an inkjet printing device can be oriented at a slant to the transport direction of the stock and thus to the printing direction. The result is that the effective distance between the nozzles transverse to the printing direction or transport direction of the substrate is reduced, which means that the print resolution can be increased.
The inkjet print heads of these matrix-like or array-like inkjet printing devices have not only the previously mentioned ink nozzles, through which printing ink can be directed onto the substrate to be printed by the inkjet print heads, but also at least one ink port and at least one control terminal. Printing ink can be supplied to the inkjet print head in question through the ink port or through each ink port, whereas a supply voltage and control signals for actuating the ink nozzles of the print head can be sent to the inkjet print head in question via the control terminal or each control terminal. In the case of the inkjet printing devices known from conventional practice, i.e., devices which have a plurality of inkjet print heads arranged in an array-like or matrix-like manner, all of the inkjet print heads are supplied individually with ink and with supply voltage and control signals. For this purpose, separate supply lines are laid from an ink reservoir and from a control device and voltage supply source to each of the individual inkjet print heads. In cases where the inkjet printing device has a large number of inkjet print heads, it quickly becomes a very complicated matter to manage and organize all these individual supply lines. It therefore also becomes difficult to manage the overall inkjet printing device, which is disadvantageous especially when it is necessary to perform service and maintenance work. The reliability of these types of inkjet printing devices is also limited by this complexity.